System for determining ambient temperature

ABSTRACT

A mechanism for indicating ambient temperature of an enclosure from temperatures determined within the enclosure. The temperatures may be obtained from two or more sensors at each of two or more locations within the enclosure. The enclosure may include an apparatus inside such as electronics of which power consumption may be determined. Data including temperatures of two locations within the enclosure at various electronics power consumption levels may be entered into a 2-D plot. An approximation of the 2-D plot may be effected with an appropriate equation to be solved for ambient temperature. The data of the 2-D plot plus temperatures of a third location and air flow levels in the enclosure may be entered into a 3-D plot. An approximation of the 3-D plot may be effected with an appropriate equation to be solved for ambient temperature.

This is a continuation of U.S. patent application Ser. No. 11/950,394,entitled “A System for Determining Ambient Temperature”, filed Dec. 4,2007, which is incorporated hereby by reference.

BACKGROUND

The present invention pertains to temperature sensing and particularlyto indirect temperature determination.

SUMMARY

The invention is a mechanism for indicating an ambient temperature aboutan enclosure containing a device, from determined temperatures withinthe enclosure.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of enclosure having possibly power consumingequipment and temperature sensors for providing temperatures from twolocations in the enclosure;

FIG. 2 is a diagram of a straight line fitted to data from sensors inthe enclosure plotted on a two-coordinate graph for determining ambienttemperature from a fitted equation;

FIG. 3 a a graph of a temperature of a first vicinity in the enclosureversus power;

FIG. 3 b a graph of a temperature of a second vicinity in the enclosureversus power;

FIG. 3 c is a graph resulting from a combining the graphs of FIGS. 3 aand 3 b into one of the first temperature of the first vicinity versusthe temperature of the second vicinity of the enclosure;

FIG. 4 is a diagram of an enclosure of equipment having sensors forproviding temperatures from three locations in the enclosure;

FIG. 4 a is a diagram of a processor with inputs from various sensorspertinent to the enclosure;

FIG. 5 a table of data from sensors for three locations in the enclosurefor various air flows and power consumption levels in the equipment inthe enclosure;

FIG. 6 is a three-coordinate graph having a plot of the data of FIG. 5which is plane-fitted with an equation;

FIG. 7 is a two-coordinate graph of cool versus warm temperatures; and

FIG. 8 is a three-coordinate graph having a plot of another set of datawhich is plane-fitted with an equation.

DESCRIPTION

Accurate ambient temperature sensing is needed in a thermostatapplication. Sensing temperature using thermistors, semiconductortemperature sensors, thermocouples or any other form of temperaturesensors from within an enclosure of electronics or equipment may resultin a temperature higher than the ambient air temperature surrounding theenclosure of the equipment or device. The term “ambient” used hereinrefers to the volume proximate to, external of and surrounding theenclosure. The difference between the ambient and the sensed temperaturemay vary and be affected by the amount of electrical energy needed topower the device, ventilation, how close or far the temperature sensorsare from warm components of the device, air flow surrounding theenclosure and/or device, device materials and their thermalconductivities, and so forth. If the amount of heat generated inside theenclosure is low and constant, constant temperature compensation mightbe sufficient. But when the heat generated inside the case or enclosureis high and variable, computing the ambient temperature may become verychallenging.

The invention may be used for enabling the device or a processor tocalculate the ambient temperature by sensing two or more differenttemperature points within the enclosure. An algorithm used to calculatethe ambient temperature may be independent of power consumption of thedevice.

Two or more temperature sensors may be placed in different locationswithin the enclosure of the device. In theory, any two locations thathave different temperatures in steady state under a given load shouldwork. In practice, one temperature sensor “T_(hot)” may be placed closeto the heat generating components. The other temperature sensor“T_(cool)” may be placed in about the coldest location within thedevice. Under very stable ambient conditions, the temperatures may besampled at different equipment or device power load conditions. Thetemperatures sampled may be used to generate equations in terms of power(by means of curve fitting). The equations may be regarded asapproximations of two-dimensional and three-dimensional relationshipswhich may be graphs, plots, representations, and/or the like.

The equations may include the following.T_(cool)=T_(ambient)+f(x)>T_(cool)=determined cool temperature. x=powerdissipated in the device. f(x)=heat rise with respect to power for thecool temperature sensor. T_(hot)=T_(ambient)+f(x)>T_(hot)=determined hottemperature. x=power dissipated in the device. f(x)=heat rise withrespect to power for the hot temperature sensor. From the system of twoequations, x and T_(ambient) are unknowns. Once these equations aresolved, T_(ambient)=f(T_(cool), T_(hot)). And since T_(cool) and T_(hot)are determined values, ambient temperature may be calculated from them.f(x) may be approximated (i.e., fitted) to a linear function, but it canalso be non-linear for increased accuracy; however, in the latter casef(x) would be more complicated to implement.

The present approach does not suggest sensing ambient temperature viaone sensor, such as a thermistor, then sensing a warm temperature viaanother sensor and calculating an error to compensate for the sensedambient temperature. The ambient temperature may be calculated from twodifferent temperatures within an enclosure of a device or equipment, andtherefore ambient temperature becomes a function of both temperatures ora function of additional temperatures if more than two sensors are used,where the additional temperatures and the initial two temperatures areaveraged together into two or three temperatures within the enclosure.

The present approach does not require special algorithms for specialcases; it may work well even if there is no heat generated within thedevice. The sought temperature is not necessarily time dependent; theambient temperature may be a function of the different temperatures andbe calculated virtually instantaneously.

The present system may use a two-dimensional (2-D) model with two ormore temperature sensors in two groups of the sensors in an enclosure ofsome equipment, or a three-dimensional (3-D) model with three or moretemperature sensors in three groups of sensors in the enclosure todetermine the ambient temperature. Each group may provide an averagetemperature of the sensors in the group. The 3-D model may also be usedto readily detect air flow. The equipment may be a piece of electronicsthat generates heat because the usage of power within the enclosurewhere the sensors are placed. Although the equipment may be inactivatedand the sensors detecting temperatures inside the enclosure of theequipment may themselves indicate the ambient temperature. Equations fordetermining ambient temperature from internal enclosure sensors may havea form of the following equation,

T _(a)=(T _(i) −aT ₂ −b)/(1−a),

where T_(a) is ambient temperature, T₁ may represent a hottertemperature and T₂ may represent a colder temperature in the enclosure14 containing equipment 27. Sensors 12 and 13 for T₁ and T₂,respectively, may be situated in two different places of the enclosure14, as shown in FIG. 1. Data may be taken and plotted on a twodimensional graph as shown in FIG. 2. A classic form of the equation fora straight line fitted to a plot of temperature data may be

y=ax+b.

From the graph, the constant “a” may be the slope and the constant “b”may be the offset of the line 11 from the zero coordinates. The“constant” nomenclature “a”, “b”, and so on, may be lower or upper case.The graph may show T₁ versus T₂ for various ambient temperatures. Theremay instead be two or more sensors situated in a vicinity representingT₁, and two or more sensors situated in another vicinity representingT₂, rather than single sensors representing T₁ and T₂, respectively. Anoutput average of the two or more sensors may be taken for T₁ and anaverage of the other two or more sensors may be taken for T₂. Anadditional third sensor or group of sensors may be used for averagingwith one or more sensors or for T₃ and for determining air flowdirection and/or magnitude. For illustrative purposes, just two sensors12 and 13 may be used in the enclosure 14. When the equipment or device27 in the enclosure 14 is energized, one may have T₁>T₂>T_(a). T₁ may beregarded as the T_(hot) and T₂ may be regarded as T_(cold). Using theequation,

T _(a)=(T _(i) −aT ₂ −b)/(1−a),

with values provided for the constants, the ambient temperature T_(a)may be determined. Values of the constants may be determined with datafrom empirical tests, simulation or calculations under conditions thatthe enclosure 14 is likely to be subject. Data may be taken from thetemperature sensors and plotted in graphs 15 and 16 in FIGS. 3 a and 3 bfor T₁ versus power and T₂ versus power, respectively. Data may be takenat different power levels of the equipment 27 in the enclosure 14. Theambient temperature may be held constant. The plots may be fitted withstraight lines. The graphs 15 and 16 may be combined into a graph 17 inFIG. 3 c. The common power determinations or measurements of the graphs15 and 16 may drop out, resulting in T₁ versus T₂ in a graph 17. Theslope value of the solid line in graph 17 may be determined andsubstituted for “a” and the offset from graph 17 may be determined,measured or calculated and substituted for “b”. One set of data as shownin FIGS. 3 a-3 c may be sufficient in a situation where the directionand magnitude of air flow, if any, remain the same for measurements ordeterminations, or are negligible, and thus the resultant equationshould be adequate in determining the ambient temperature T_(a). Whereair flow is changed, then a new set of data, like that in FIGS. 3 a and3 b, should be taken for the equipment 27 of enclosure 14 situated inthe new air flow. The new air flow may result in a different line(dashed) 19 in graph 17 of FIG. 3 c.

The two-dimensional approach just noted herein may be extended to athree-dimensional approach with a third sensor 18 situated in theenclosure 14, as illustratively shown in FIG. 4. FIG. 4 a shows aprocessor 37 which may determine an ambient temperature proximate to theenclosure 14 based on outputs from temperature sensors 12, 18 and 13, anair flow sensor 35 proximate (external and/or internal) to theenclosure, and a power level sensor 36 connected to a power input to theelectronics equipment 27 and/or processor 37. The ambient temperaturemay be indicated at an output 38 of the processor 37 or electronics 27.Electronics 27 or processor 37 may be configured for either thetwo-dimensional approach and/or the three-dimensional approach as notedherein. Processor 37 may be internal or external to enclosure 14.

The 3-D approach may result in an equation which accommodates variousair flows. The resultant plot of the data may result in a 3-D surface.The simplest form of this surface is a plane of a 3-axis coordinatesystem. The basic equation form may be

ax+by+cz+d=0.

For improved accuracy, a more complicated non-linear 3-D surfaceequation may be generated from the data. Three temperature readings forT₁ sensor 12, T₂ sensor 13 and T₃ sensor 18 may be taken for each powerlevel at various air flows or vice versa. The ambient temperature shouldbe constant during the data taking.

For an illustrative example of data taking and determining the values ofthe constants for the three equations of the three-dimensional approach,one may note tables of FIG. 5. Each sensor and respective temperaturemay represent a coordinate axis of a 3-axis or 3-D graph 24 in FIG. 6.In table 21, temperature determinations or measurements T₁, T₂ and T₃from sensors 12, 13 and 18 for a first air flow and a first power levelmay be 85, 78 and 74 degrees F., respectively; for the first air flowand second power level, the determinations or measurements may be 88, 79and 76 degrees, respectively; and for the first air flow and third powerlevel, the determinations or measurements may be 89, 84 and 79,respectively. In table 22, temperature determinations or measurementsT₁, T₂, and T₃ from sensors 12, 13 and 18 for a second air flow and thefirst power level may be 80, 76, and 71 degrees, respectively; for thesecond air flow and the second power level, the determinations ormeasurements may be 84, 78 and 75 degrees, respectively; and for thesecond air flow and the third power level the determinations ormeasurements may be 86, 81 and 77 degrees, respectively. In table 23,temperature determinations or measurements T₁, T₂, and T₃ from sensors12, 13 and 18 for a third air flow and the first power level, thedeterminations or measurements may be 91, 80 and 76 degrees,respectively; and for the third air flow and the second power level thedeterminations or measurements may be 93, 84, and 78 degrees,respectively; and for the third air flow and the second power level, thedeterminations or measurements may be 95, 88 and 82 degrees,respectively.

Since the ambient temperature (T_(a)) may be regarded as at 70 degreesF., during data determination or a taking of the empirical measurements,the data may be adjusted for T_(a), resulting in data points forplotting on the 3-coordinate graph 24, as illustrated in FIG. 6. Thedata points may be 15, 8, 4; 18, 9, 6; and 19, 14, 9; for air flow 1 andpower levels 1, 2 and 3, respectively. Data points may be 10, 6, 1; 14,8, 5; and 16, 11, 7; for air flow 2 and power levels 1, 2 and 3,respectively. Data points may be 21, 10, 6; 23, 14, 8; and 25, 18, 12;for air flow 3 and power levels 1, 2 and 3, respectively. The datapoints from 15, 8, 4 through 25, 18, 12, as indicated herein, may belabeled A, B, C, D, E, F, G, H and I, respectively. The latter labelsmay be used in graph 24. One may plane fit the data points and come upwith a plane 26 and a corresponding equation. These data points may beinserted in versions of the following equation,

ax+by+cz+d=0,

to obtain values for the respective constants for the ultimate equationfor obtaining T_(a) from T₁, T₂ and T₃ at various air flows and powerlevels of the enclosure 14 and equipment 27.

For an illustrative example, with respect to the 2-D model, thefollowing temperatures were logged at 70 degrees F. ambient condition.These are at 3 different load conditions. The cool temperatures are73.95439, 74.14308 and 74.80374 degrees F. The warm temperatures are81.49281, 82.11406 and 84.3687. From these temperatures, one maysubtract temperatures from ambient and graph. The results from the cooltemperatures are 3.95439, 4.14308 and 4.80374. The results from the warmtemperatures are 11.49281, 12.11406 and 14.3687. The results for bothsets of temperatures may be plotted as coordinate points 33 a graph 31of FIG. 7. One may generate a best curve fit 32. In this condition, ithappens to be linear.

T _(warm) −T _(ambient) =A*(T _(cool) −T _(ambient))+B,

where A=2.9468 and B=0. One may look to the plot 33 and linear curve 32fitting in graph 31 of FIG. 7. One may haveT_(ambient)=(T_(warm)A*(T_(cool)−B)/(1−A). After applying this equationto the original temperature, the calculated ambient temperatures are70.08218, 70.04868 and 69.89057, respectively. As may be seen, thetemperatures appear accurate. And since the above items have been theextreme load conditions, different loads in between would generatetemperatures that fall on the same curve and therefore the ambienttemperature can be recovered. When the same device is exposed todifferent ambient temperatures, the temperature rise on the sensors isconstant and the ambient temperature may be recovered. With an exampleat ambient temperature=80 degrees, one may get cool temperatures of84.03199, 83.59956 and 84.8985, and hot temperatures of 92.10085,91.00635 and 94.71613. The calculated temperatures may be 79.88731,79.79496 and 79.85554, respectively.

With respect to a 3-D model, three given different temperature sensorswill generate a 3-D surface equation, in the case of a linear approach,this would be a plane. For example, Ax+By+Cz+D=0. Assuming that theplane crosses at (0,0,0), which means if no heat is generated within thedevice, then the temperature sensed by the sensors=ambient. Ax+By+Cz=0,x,y,z are T₁−T_(ambient), T₂−T_(ambient), and T₃−T_(ambient),respectively.

T _(Ambient)=(A*T ₁ B*T ₂ C*T ₃)/(A+B+C),

where A, B and C are plane constants, and may be calculatedalgebraically or by the use of curve/surface fit software. In somecases, temperatures inside an enclosure might be affected by externalenvironmental changes and a 2-D solution might not be sufficient torecover ambient temperature accurately. For instance, airflow directionor speed may cause some variation and constantly generate temperaturesthat do not fall on a 2-D dimensional curve. With a third sensor,temperature variations may be modeled with a surface of 3-D equation. Agraph 41 in FIG. 8 shows an example of that. In this example, the points42 are surface fit to a plane 43, instead of a 2-D curve or a line 32 asin FIG. 7.

Determinations, measurements, plotting, graphs, curve-, line- andplane-fitting, calculations, approximations, relationships,representations, managing equations and getting solutions, obtainingvalues for constants and temperatures such as ambient, doing flow andpower level determinations or measurements, and other items foreffecting the present system, and so forth, may be effectedelectronically with a processor or the like, along with appropriatesoftware as desired or needed.

In the present specification, some of the matter may be of ahypothetical or prophetic nature although stated in another manner ortense.

Although the invention has been described with respect to at least oneillustrative example, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentspecification. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. A device comprising: a housing; one or more heat generating elements within the housing, wherein during operation of the device, the one or more heat generating elements cause a first region within the housing to be warmer than a second region within the housing; a first temperature sensor for reporting a measure that is related to the temperature in the first region; a second temperature sensor for reporting a measure that is related to the temperature in the second region; a controller in communication with the first temperature sensor and the second temperature sensor, the controller determining a measure related to an ambient temperature outside of the housing based, at least in part, on the measure that is related to the temperature in the first region reported by the first temperature sensor and the measure that is related to the temperature in the second region reported by the second temperature sensor; and the controller outputting the measure related to the ambient temperature.
 2. The device of claim 1, wherein the device is powered, at least in part, by electrical energy, and wherein the one or more heat generating components generate heat by consuming the electrical energy.
 3. The device of claim 2, wherein a level of the electrical energy needed to power the device changes over time.
 4. The device of claim 3, wherein the measure related to the ambient temperature determined by the controller is relatively independent of the level of the electrical energy needed to power the device.
 5. The device of claim 1, wherein the controller determines the measure related to the ambient temperature outside of the housing based, at least in part, on a predetermined relationship between the measure related to the ambient temperature outside of the housing, the measure related to the temperature in the first region reported by the first temperature sensor and the measure related to the temperature in the second region reported by the second temperature sensor.
 6. The device of claim 5, wherein the device is powered by a level of electrical energy that changes over time, and wherein the measure related to the ambient temperature determined by the controller is relatively independent of the level of the electrical energy powering the device.
 7. The device of claim 5, wherein the predetermined relationship includes a linear relationship.
 8. The device of claim 5, wherein the predetermined relationship includes a non-linear relationship.
 9. The device of claim 5, wherein the predetermined relationship includes a two-dimensional relationship.
 10. The device of claim 5, wherein the predetermined relationship includes a three or more dimensional relationship.
 11. The device of claim 1, wherein the device is powered by a level of electrical energy that changes over time, and wherein the device includes one or more sense elements for sensing a measure that is related to the level of electrical energy powering the device.
 12. The device of claim 11, wherein the controller determines the measure related to the ambient temperature outside of the housing based, at least in part, on a predetermined relationship between the measure related to the ambient temperature outside of the housing, the measure related to the temperature in the first region reported by the first temperature sensor, the measure related to the temperature in the second region reported by the second temperature sensor, and the measure related to the level of electrical energy powering the device.
 13. The device of claim 1 further comprising: a third temperature sensor for reporting a measure that is related to the temperature in a third region within the housing; the controller determining a measure related to an air flow direction and/or air flow magnitude about the housing that is based, at least in part, on the measure related to the temperature in the third region reported by the third temperature sensor; and the controller using the measure related to the air flow direction and/or air flow magnitude about the housing when determining the measure related to the ambient temperature outside of the housing.
 14. A device comprising: a first temperature sensor situated at a first location in a housing; a second temperature sensor situated at a second location in the housing that is spaced from the first location; a controller receiving a first temperature from the first temperature sensor and a second temperature from the second temperature sensor; and wherein the controller determines a measure related to ambient temperature outside of the housing based, at least in part, on the first temperature and the second temperature.
 15. The device of claim 14, wherein the controller outputs the measure related to ambient temperature.
 16. The device of claim 14 further comprising: a third temperature sensor situated at a third location in the housing; the controller receiving a third temperature from the third temperature sensor; and wherein the controller determines the measure of ambient temperature outside of the housing based, at least in part, on the first temperature, the second temperature and the third temperature.
 17. The device of claim 14 further comprising: a sense element for sensing a measure related to a level of power consumed by at least part of the device; and the controller determining the measure of ambient temperature outside of the housing based, at least in part, on the first temperature, the second temperature and the measure related to the level of power consumed by at least part of the device.
 18. A device comprising: an enclosure; and a controller for determining a measure related to an ambient temperature outside of the enclosure based, at least in part, on a relationship between a first temperature inside of the enclosure and a second temperature inside of the enclosure.
 19. The device of claim 18, further comprising: a first temperature sensor for sensing the first temperature inside of the enclosure; and a second temperature sensor for sensing the second temperature inside of the enclosure.
 20. The device of claim 19, wherein the first temperature sensor is situated in a first region inside of the enclosure and the second temperature sensor is situated in a second region inside of the enclosure, wherein during operation of the device, the first region is warmer than the second region.
 21. A device comprising: a first temperature sensor situated in a housing; a sense element for sensing a measure related to a level of power consumed by at least part of the device; a controller receiving a first temperature from the first temperature sensor and the measure related to the level of power consumed by at least part of the device from the sense element; and the controller is configured to determine a measure related to the ambient temperature outside of the housing based, at least in part, on the first temperature received from the first temperature sensor and the measure related to the level of power consumed by at least part of the device received from the sense element.
 22. The device of claim 21, further comprising: a second temperature sensor situated in the housing; the controller receiving a second temperature from the second temperature sensor; and wherein the controller is configured to determine the measure related to the ambient temperature outside of the housing based, at least in part, on the first temperature received from the first temperature sensor, the second temperature received from the second temperature sensor, and the measure related to the level of power consumed by at least part of the device received from the sense element.
 23. The device of claim 21, further comprising: an air flow sensing element for sensing a measure that is related to the air flow about the housing; and wherein the controller is configured to determine the measure related to the ambient temperature outside of the housing based, at least in part, on the first temperature received from the first temperature sensor, the measure that is related to the air flow about the housing received from the air flow sensing element, and the measure related to the level of power consumed by at least part of the device received from the sense element.
 24. A device comprising: a first temperature sensor situated in a housing; an air flow sensing element for sensing a measure that is related to the air flow about the housing; a controller receiving a first temperature from the first temperature sensor and the measure related to the air flow about the housing from the air flow sensing element; and the controller is configured to determine a measure related to the ambient temperature outside of the housing based, at least in part, on the first temperature received from the first temperature sensor and the measure related to the air flow about the housing from the air flow sensing element.
 25. The device of claim 24, wherein the air flow sensing element includes a temperature sensor that is separate from the first temperature sensor.
 26. The device of claim 24, wherein the air flow sensing element senses a measure related to an air flow direction and/or air flow magnitude about the housing.
 27. A device comprising: an enclosure; and a controller for determining a measure related to an ambient temperature outside of the enclosure based, at least in part, on a measure related to the difference between a first temperature inside of the enclosure and a second temperature inside of the enclosure.
 28. The device of claim 27, further comprising: a first temperature sensor located in the enclosure for sensing the first temperature; and a second temperature sensor located in the enclosure for sensing the second temperature, wherein the second temperature sensor is spaced from the first temperature sensor.
 29. The device of claim 28, wherein the first temperature sensor is situated in a first region inside of the enclosure and the second temperature sensor is situated in a second region inside of the enclosure, wherein during operation of the device, the first region is warmer than the second region.
 30. The device of claim 29, further comprising: a third temperature sensor located in the enclosure for sensing a third temperature; and wherein the controller is configured to determine the measure related to the ambient temperature outside of the enclosure based, at least in part, on a measure related to the difference between the first temperature inside of the enclosure and the second temperature inside of the enclosure, as well as the third temperature. 